In semiconductor manufacturing, many types of gases are used in different ways. For example, a number of different types of gases are drawn, not all at once but one after another in a series fashion by switching the gas type from one to another at specific time intervals. Also, one and the same type of gas is often used at different flow rates simultaneously or in parallel. In those applications, the flow rates must be controlled with high accuracy.
In prior art gas feeding apparatuses for use in semiconductor manufacturing, flow rate controllers such as mass flow rate controllers are installed, one on each gas line, to control the flow rate with high accuracy.
In etching, one of the important processes in semiconductor manufacturing, for example, a plurality of insulating films are etched. This process is made up of a number of etching steps. In each step, 3 or 4 types of gases are used in combination. To supply those gases, prior art gas feeders require a total of more than 10 gas and flow rate controllers in the etching process alone. A vast number of such controllers have to be installed to serve an entire semiconductor manufacturing plant.
In the Chemical Vapor Deposition (CVD) process, a type of gas is supplied to a treatment reactor at one or different flow rates through a plurality of outlets simultaneously to carry out a CVD treatment. The prior art gas feeder has a flow rate controller installed at every outlet line to regulate the flow rates. Here, also, too many flow rate controllers are needed. To a single treatment reactor for the CVD process, in addition, a plurality of types of gases may also be supplied in a series fashion. That likewise requires quite a number of flow rate controllers.
Heretofore, mass flow rate controllers had been the primary flow rate controllers used. In recent years, so-called pressure-type flow control systems have become more common.
The installation of a large number of flow rate controllers not only increases the size of the gas feeder but also makes it difficult to keep down the costs both of the feeder itself and of facility maintenance and service costs. This also presents such problems as increased labor in maintenance and the necessity of keeping many replacement and spare parts in stock, which inevitably raises the running costs of the gas feeder.
The present invention addresses those problems encountered with the prior art apparatuses and methods for feeding gases in semiconductor manufacturing plants, that is, the necessity of installing too many flow rate controllers, one for each outlet line, which has prohibited size reduction of the gas feeding equipment and reduction of the costs of the equipment itself.